Hygroscopicity and cloud condensation nucleus activity of atmospheric aerosol particles at urban and forest sites and their contribution to cloud droplet formationHygroscopicity and cloud condensation nucleus activity of atmospheric aerosol particles at urban and forest sites and their contribution to cloud droplet formation都市・森林域における大気エアロゾル粒子の吸湿性・雲凝結核活性およびそれらの雲粒形成への寄与